1. Technical Field
The present invention relates to a liquid jet head, a liquid jet apparatus, and a method of manufacturing a liquid jet head capable of ejecting droplets onto a recording medium for recording.
2. Related Art
An ink jet type liquid jet head used in recent years ejects ink droplets onto recording paper or the like to record characters or figures thereon, or ejects liquid material onto a surface of an element substrate to form a functional thin film. According to this system, liquid such as ink and liquid material is introduced to channels from a liquid tank via supply pipes. Then, the liquid is ejected from nozzles communicating with the channels with application of pressure to the liquid charged into the channels. In delivery of the liquid, the liquid jet head and/or the recording medium are shifted to record characters or figures, or to form a functional thin film having a predetermined shape.
A through flow type is known as this type of liquid jet head. The through flow type liquid jet head constantly circulates liquid contained within the channels by using a piezoelectric element for constituting walls defining the channels. The through flow type rapidly discharges bubbles or foreign matters to the outside of the channels when bubbles or foreign matters are mixed into the liquid. Accordingly, maintenance of the through flow type is allowed without the use of a cap structure or a service station. As a result, the consumption of the liquid during maintenance decreases, and the running cost lowers. In addition, wasteful consumption of a recording medium produced by inferior delivery decreases to the minimum.
JP 2003-505281 W discloses a liquid circulation type liquid jet head. FIG. 15A illustrates a liquid jet head disclosed in JP 2003-505281 W. A piezoelectric element includes two PZT wafers 30 and 32, and a polyimide sheet 38 sandwiched between the two PZT wafers 30 and 32. Grooves are formed in each inner surface of the PZT wafers 30 and 32. The respective grooves in the PZT wafer 30 face to the corresponding grooves in the PZT wafer 32 to define chambers 36. Electrodes 44 and 46 are provided on the side surfaces of the grooves of the PZT wafers 30 and 32, respectively. The electrodes 44 and 46 drive, in a shearing mode, side walls 48 formed between the adjoining chambers 36. Each of the chambers 36 is divided into an upper part and a lower part by the polyimide sheet 38. The polyimide sheet 38 is cut at ends 50 closest to nozzles 42. Liquid such as ink circulates from an upper chamber to a lower chamber as indicated by an arrow 52.
FIG. 15B is a perspective view illustrating another type of disassembled liquid jet head disclosed in JP 2003-505281 W. The liquid jet head includes PZT wafers 88 and 89, a mask plate 100, an opening plate 66, and a nozzle plate 64. The PZT wafers 88 and 89 are constituted by two piezoelectric elements overlapped with each other, and form three types of flow paths 90, 92, and 94. The mask plate 100 has openings communicating with the flow paths 90 and the flow paths 94, and closes the flow paths 92. The opening plate 66 has opening portions extending over the flow paths 92 and connecting the flow paths 90 and flow paths 94 such that the flow paths 90 and flow paths 94 can communicate with each other. The nozzle plate 64 has nozzles 102 communicating with the opening portions of the opening plate 66. Liquid flows from the flow paths 90 via the opening portions of the opening plate 66 toward the flow paths 94 as indicated by the arrow 52. In other words, liquid circulates around the flow paths 92. Line electrodes are provided on side surfaces of each pair of walls 96 and 98. The side surfaces of the walls 96 and 98 provided with the line electrodes are located on the flow path 92 side. On the other hand, earth electrodes are provided on the other side surfaces of each pair of the walls 96 and 98. The other side surfaces of the walls 96 and 98 provided with the earth electrodes are located on the flow paths 90 and 94 side. These line electrodes and earth electrodes drive the walls 96 and 98 to eject small droplets 49 from the nozzles 102.
JP 2011-131533 A discloses another type of liquid circulation type liquid jet head. This liquid jet head includes a piezoelectric plate, a cover plate, and a nozzle plate. The piezoelectric plate contains a plurality of grooves in the front surface of the piezoelectric plate. The cover plate is bonded to the front surface of the piezoelectric plate, and covers upper openings of the respective grooves. The nozzle plate is disposed on the side surface of the piezoelectric plate, and has a plurality of nozzles communicating with the respective grooves. The cover plate has a liquid supply hole to supply liquid to the respective grooves via the liquid supply hole. A plurality of discharge paths in correspondence with the respective grooves are formed in the front surface of the nozzle plate on the piezoelectric plate side. The liquid jet head further includes a flow path member disposed on the rear surface of the piezoelectric plate. The flow path member contains a liquid discharge chamber. The discharge paths formed in the nozzle plate connect the grooves formed in the front surface of the piezoelectric plate and the liquid discharge chamber formed in the rear surface of the piezoelectric plate such that the grooves and the liquid discharge chamber communicate with each other. Liquid flowing from the liquid supply hole branches into the respective grooves, passes from the respective grooves through the corresponding discharge paths, and joins at the liquid discharge chamber.
The piezoelectric elements of the liquid jet head shown in FIG. 15A requires the polyimide sheet 38 disposed between the two PZT wafers, and the cuts at the ends 50 of the polyimide sheet 38 at positions corresponding to the nozzle positions. This structure increases the number of parts, and requires alignment between the grooves formed in the two PZT wafers 30 and 32, and alignment of the cuts of the polyimide sheet 38 with the respective grooves. In this case, the number of parts increases, and the assembling steps become complicated. Moreover, the liquid jet head shown in FIG. 15B requires a plurality of the flow paths constituted by units of the flow paths 90, 92 and 94 and formed in the two PZT wafers overlapped with each other. The liquid jet head further requires the mask plate 100 on the end surfaces of the flow paths 90, 92, and 94, the opening plate 66 on the upper surface of the mask plate 100, and further the nozzle plate 64 on the upper surface of the opening plate 66. Accordingly, the liquid jet head shown in FIG. 15B is constituted by a large number of parts, and has a complicated structure requiring accurate alignment at the time of assembly. The liquid jet head disclosed in JP 2011-131533 A requires the same number of the discharge paths as the number of the nozzles, and forms the discharge paths in the front surface of the nozzle plate on the piezoelectric plate side with the same pitch as the pitch of the nozzles. In this case, the structure becomes complicated, and the manufacture becomes extremely difficult.